A subquery in an SQL SELECT statement is enclosed in:

Option A: braces -- {...} - Braces are not used to enclose subqueries in SQL SELECT statements. This option is incorrect.
Option B: CAPITAL LETTERS - Capital letters are not used to enclose subqueries in SQL SELECT statements. This option is incorrect.
Option C: parenthesis -- (...) - This option is correct. Subqueries in SQL SELECT statements are enclosed in parentheses to distinguish them from the main query.
Option D: brackets -- [...] - Brackets are not used to enclose subqueries in SQL SELECT statements. This option is incorrect.
Conclusion:
In SQL, a subquery in a SELECT statement is enclosed in parentheses to separate it from the main query and to specify its scope. Therefore, the correct answer is Option C: parenthesis -- (...).